WPF - Set binding in Child UserControl from Parents pure XAML - wpf

Question

I have browsed the InterWebs enough! I place my hope of resolving this issue here.
I have two parent UserControls, ParentUc1 and ParentUc2. They both include a ChildUc.
Without adding any code except for XAML code, I would like to set the values of the SensorRotationAngle binding in the ChildUc from each of the Parents.
ParentUc1:
Set SensorRotationAngle to 10
ParentUc2:
Set SensorRotationAngle to 20
ChildUc:
<Rectangle>
<Rectangle.RenderTransform>
<RotateTransform Angle="{Binding SensorRotationAngle}" />
</Rectangle.RenderTransform>
</Rectangle>
Thanks!

Answer 1

Since your child user control gets the value from a binding to the SensorRotationAngle property you need to ensure that the DataContext class which is set on your ChildUc has such a property.
So, you could create your child control like this, directly instanciate the view model and set the value of SensorRotationAngle in the process:
<ChildUc>
<ChildUc.DataContext>
<ChildUcViewModel SensorRotationAngle="30"></ChildUcViewModel>
</ChildUc.DataContext>
</ChildUc>
The view model itself could like this:
public class ChildUcViewModel : INotifyPropertyChanged
{
public int SensorRotationAngle
{
get
{
return _sensorRotationAngle;
}
set
{
if (_sensorRotationAngle != value)
{
_sensorRotationAngle = value;
OnPropertyChanged();
}
}
}
int _sensorRotationAngle;
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
I just tested this on my system, it works.

Answer 2

I believe this is a case of using Value inheritance power from DependencyProperty.
Basically, the childcontrol will inherit the value from the parent control SensorRotationAngle value directly.
public class ParentControlGrid : Grid
{
// Dependency Property
public static readonly DependencyProperty SensorRotationAngleProperty =
DependencyProperty.Register("SensorRotationAngle", typeof(int),
typeof(ParentControlGrid), new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.Inherits));
// .NET Property wrapper
public int SensorRotationAngle
{
get { return (int)GetValue(SensorRotationAngleProperty); }
set { SetValue(SensorRotationAngleProperty, value); }
}
}
public class ChildControlTextBox : TextBox
{
// Dependency Property
public static readonly DependencyProperty SensorRotationAngleProperty;
static ChildControlTextBox()
{
SensorRotationAngleProperty = ParentControlGrid.SensorRotationAngleProperty.AddOwner(typeof(ChildControlTextBox),
new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.Inherits));
}
// .NET Property wrapper
public int SensorRotationAngle
{
get { return (int)GetValue(SensorRotationAngleProperty); }
set { SetValue(SensorRotationAngleProperty, value); }
}
}
<Window x:Class="WpfTestProj.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:wpfTestProj="clr-namespace:WpfTestProj"
Title="MainWindow" Height="350" Width="525">
<wpfTestProj:ParentControlGrid SensorRotationAngle="500">
<wpfTestProj:ChildControlTextBox Text="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=SensorRotationAngle}" />
</wpfTestProj:ParentControlGrid>